SHP Big Block Cam Spec's

[Warren F.]

I found that the previous discussion on this subject, has opened up a new area of questions for me.

In Colvin's book "Corvette by the Numbers", he lists spec's for the '65,'66,'67,'68,'69 & '71 big block camshafts. I am particularly interested in discussing the specs for the L78, L72, L71 & LS6, mainly because these were street engines.

What I find interesting is that the '65,'66 & '69 camshaft list part # 3863143. While '67,'68 & '71 camshaft list part # 3904366.

What is confusing to me, is that the camshaft for '65, '66 & '69 all have different spec's from each other. Different lifts, both intake & exhaust, different durations (except '66) both intake & exhaust.

Yet, the '67, '68, '69 & '71 camshafts have the same spec's, but two different camshaft #'s are used?

And how can the '65 & '66 camshafts have the same part # with different specifications?

I am also interested in knowing which camshaft of the three different
spec's listed :ie the '65 L78, '66 L72 & the '67 L71 would make the most power, all other engine spec's being the same (same cfm, intake style, combustion chamber style/volume, compression, etc). Because I don't understand whether greater lift is more advantageous or longer duration, is.

And last how can the '67,'68,'69 L71 & '71 LS6 have the same spec's but different camshaft part #?

I find these mysteries intriguing, somehow.

[Michael H.]

Re: Solved

Warren,

I think we were all very confused for many years on this issue but yesterday, Matt Purdy posted something that finally straightened everything out. (see the original discussion of "427 valve lash", Saturday, 9 Oct and "this weeks assignment" Sunday, 10 Oct) Matt found the original prints on the 3863143 cam and discovered that the correct intended valve lash settings are .024/.028, not the .020/.024 that was shown in the 65-66 service and owners manual. This would account for some of the differences in cam timing spec's shown in various publications of that time. These same lift/duration specifications continued on for that cam from 65 to 71 with no change.

The other very confusing part was the 2nd part number that became available for the introduction of the 1967 model year. This revised cam, part number 3904366, was, as John Hinckley explained, exactly the same as the original 3863143 but it did not have the grooved rear cam journal. (whole nuther story) This 3904366 number was listed in later Chevelle and Camaro parts books but for some reason, was never shown in the Corvette parts books. Only the 143 was listed in Corvette parts books. So, the Corvette parts book should have listed;

3863143.....Cam, 65-66 Corvette, 396, 427

3904366.....Cam, 67-69, 71 Corvette 427, 454

I would have to guess that the entire confusing problem with lash, cam specs and application was due to errors in several publications, starting in 65.

Michael

[Warren F.]

Re: Solved

Michael:

Thanks, for the explanation. I understand it better now.